1. Field of the Invention
The present invention relates to a method for determining a track-cross direction of a pick-up head of an optical disk drive, and more particularly, to a method that uses two different deciding methods to determine the track-cross direction of the pick-up head.
2. Description of the Prior Art
Each CD (Compact Disc) drive or DVD (Digital Versatile Disc) drive has a pick-up head for reading data from an optical disc or writing data onto the optical disc. Every time when the pick-up head executes the reading operation or the writing operation, the pick-up head must first move to a target track on the optical disc so that the up heads can start to read data or write data. The search operations can be classified into the short distance cross-track operation and the long distance cross-track operation according to a distance between the present position of the pick-up head and the target track position. The pick-up head is installed on a movable sled. The sled is driven by a sled motor. A velocity of the sled (identical to a track-cross velocity of the pick-up head) is decided according to which kind of track-cross operation (the short distance cross-track operation or the long distance cross-track operation). When the pick-up head executes a short distance track-cross operation, the sled and the pick-up head move with a low velocity. This is because if the pick-up head moves too fast, the pick-up head maybe easily overshoot the target track. When the pick-up head executes a long distance cross-track operation, the velocity of the sled and the pick-up head must be accelerated to a certain velocity and then decelerated to a low velocity so that the pick-up head can arrive the target track within a certain time.
No matter if the pick-up head executes the short distance track-cross operation or the long distance track-cross operation, the pick-up head must arrive at the target track correctly and quickly (or arrive at the target track with a predetermined time). The distance between two neighboring tracks becomes shorter as data density on optical discs increases. The access rate of the optical disc drive also gets faster and faster. So, how to decrease time taken on track crossing is still a major topic.
No matter if the pick-up head executes the short distance track-cross operation or the long distance track-cross operation, the velocity and the direction of the pick-up head relative to the optical disc are important parameters of track-cross control. After determining the track-cross direction of the pick-up head, the optical disc drive is able to control the sled motor to move the pick-up head to the target track.
For example, when the optical disc drive executes the track-cross operation, the optical disc drive constantly determines the track-cross direction of the pick-up head. The prior optical disc drive uses different methods to determine the cross-track direction according to the track-cross velocity of the pick-up head. When the pick-up head moves in low speed, the optical disc drive determines the track-cross direction of the pick-up head according to a phase difference between a RFRP (radio frequency ripple) signal and a tracking error (TE) signal. The RFRP signal is defined as the difference between the peak envelope and the bottom envelope of the RF signal when the pick-up head emits a laser beam to the pit portion or the land portion of the track on the optical disc. The tracking error signal represents whether the pick-up head is located at the center of the target track. Frequencies of the RFRP signal and the tracking error signal are related to the track-cross velocity of the pick-up head. If the track-cross velocity of the pick-up head is fast, the frequencies of the RFRP signal and the tracking error signal is high. When the track-cross velocity of the pick-up head becomes faster, an error will be generated if the phase difference between the two signals is used to determine the cross-track direction of the pick-up head. Therefore, when the cross-track velocity of the pick-up head is changed from low to high, the optical disc drive continuously determines that the track-cross direction of the pick-up head remains unchanged instead of using the phase difference to determine the track-cross direction of the pick-up head, so as to prevent the error. When the track-cross velocity of the pick-up head changes from high to low, the optical disc drive uses the phase difference method to determine the track-cross direction again.
Therefore, the determination of the track-cross velocity of the pick-up head is very important in track-cross control. If the determination result of the track-cross velocity is wrong, the optical disc drive is unable to use the correct method to determine the track-cross direction. Once the determination result of the track-cross direction is wrong, the whole track-cross operation fails and the optical disc drive is unable to execute certain operations.
The prior optical disc drive uses single means to determine the track-cross velocity of the pick-up head (such as a RFZC signal). The single means easily generates an error due to glitch or defect (such as scratch). This error causes the wrong determination of the track-cross velocity.
It is therefore a primary objective of the claimed invention to provide a method that uses two different techniques to determine the track-cross direction of the pick-up head, so as to solve the problem of the prior art.
The claimed invention, briefly summarized, discloses a method for determining a track-cross direction of a pick-up head of an optical disk drive. The method comprises the following steps. (1) When a track-cross velocity of the pick-up head was determined to be greater than a predetermined velocity, the track-cross velocity of the pick-up head is determined to be changed less than the predetermined velocity. If not, the track-cross direction remains unchanged. (2) When the track-cross velocity of the pick-up head was determined to be less than the predetermined velocity, it is further determined whether the track-cross velocity of the pick-up head is changed to be greater than the predetermined velocity. If not, the track-cross direction is determined according to a phase difference between a first track-cross signal and a second track-cross signal.
It is an advantage of the claimed invention that the claimed invention uses two different techniques to confirm the track-cross velocity of the pick-up head. Therefore, the claimed invention can prevent a wrong determination generated by a glitch and missed signals. The optical disc drive applying the present invention can therefore control the track-cross operation of the pick-up head correctly.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.